1. Field of the Invention
The invention relates to a power generation device that drives a power generator by increasing speed of rotation of a main shaft due to an external force, by use of a speed increaser.
2. Description of Related Art
Conventionally, as a wind turbine generator in which a main shaft is rotated to generate power when blades receive wind, there has been a wind turbine generator that includes a speed increaser. The speed increaser drives a power generator by increasing speed of rotation of the main shaft. As shown in FIG. 7, this type of speed increaser 202 includes a planet gear mechanism 203, a high-speed range gear mechanism 204, and an output shaft 205. Rotation of a main shaft 200 is input to the planet gear mechanism 203 that then increases a speed of the rotation of the main shaft 200. The rotation, speed of which has been increased by the planet gear mechanism 203, is input to the high-speed range gear mechanism 204 that further increases speed of the rotation. The output shaft 205 outputs rotation, speed of which has been increased by the high-speed range gear mechanism 204. A drive shaft 212 of a power generator is connected to the output shaft 205, and a rotor (not shown) of the power generator is fitted to the drive shaft 212.
In the planet gear mechanism 203, upon rotation of an input shaft 203a that is connected to the main shaft 200, to which blades (not shown) are fitted, so that the input shaft 203a is rotatable together with the main shaft 200, a planet carrier 203b rotates. Thus, a sun gear 203d is rotated at increased speed through a planet gear 203c. Then, this rotation is transmitted to a low-speed shaft 204a of the high-speed range gear mechanism 204. In the high-speed range gear mechanism 204, as the low-speed shaft 204a rotates, an intermediate shaft 204d is rotated at increased speed through a low-speed gear 204b and a first intermediate gear 204c, and further, the output shaft 205 is rotated at increased speed through a second intermediate gear 204e and a high-speed gear 204f. In the speed increaser 202, a number of roller bearings 206 to 211 are used as bearings that support the low-speed shaft 204a, the intermediate shaft 204d, and the output shaft 205, respectively, so that the low-speed shaft 204a, the intermediate shaft 204d, and the output shaft 205 are rotatable (for example, see Japanese Patent Application Publication No. 2007-232186 (JP 2007-232186 A)).
In the conventional wind turbine generator, there has been a problem that smearing (a phenomena in which seizure of surface layers occurs) is caused on rolling contact surfaces of rollers, and raceway surfaces of rotating rings in the roller bearings 210 and 211 supporting the output shaft 205 that rotate at high speed, and service lives of the roller bearings 210 and 211 are shortened. Smearing described above is thought to occur not only in the wind turbine generator, but also on roller bearings provided in a power generation device of a different model, in which a power generator is driven while speed of rotation of a main shaft is increased by using a speed increaser.
The present inventors have pursued extensive studies on a mechanism by which smearing occurs. As a result, the following findings have been obtained. When rotation speed of a main shaft is decreased sharply due to a reduction of external force (force of wind), rotation speed of a drive shaft of a power generator that rotates together with a rotor is prone to exceed rotation speed of an output shaft of a speed increaser due to inertia of the rotor of the power generator having a large weight. Accordingly, so-called torque release (load release) occurs in the output shaft, and a radial load acting on a roller bearing that supports the output shaft is reduced due to the torque release. As a result, in the roller bearing, sliding friction resistance and the like between the roller and a cage that retains the roller becomes larger than rolling friction resistance between the roller and a rotating ring, and accordingly, rotation of the roller about its own axis is delayed. Then, when rotation speed of the main shaft is increased sharply from this state due to an increase in external force (force of wind), inertia torque of the rotor due to increased speed is applied to the output shaft, and a radial load acting on the roller bearing that supports the output shaft is increased sharply. In that moment (in a transitional state), sliding occurs between the roller and the rotating ring in a state where a high load is acting on the roller, and temperature of a contact surface between the roller and the rotating ring is increased, thereby causing smearing. The present invention has been completed based on the findings.